The present invention generally relates to a balloon catheter such as one for conducting dilatation procedures within the vascular system and in conjunction with a guidewire along which the balloon catheter is slidably moved for positioning and treatment. The balloon catheter incorporates an inner tube for receiving the guidewire therewithin. A distal portion of the inner tube has a securement location at which a distal leg of the balloon is secured to the inner tube. A relatively long tip of the catheter extends distally beyond this securement location. This tip has an external annular chamfer, which can be in combination with an internal annular taper. The result is improved tracking for situations and for guidewire and balloon catheter combinations which present tracking problems due to stiffer catheter distal portions, particularly when used with guidewires which allow for and provide curves of tighter radii within body vessels.
In certain balloon applications, components are included which increase the stiffness and generally reduce the bendability or flexibility at those distal portions of the balloon catheter which need to easily track an inserted guidewire along its tortuous path. Often, this tortuous path is provided by the thinner variety of guidewires, such as those used in coronary angioplasty or PTCA procedures. Stent delivery balloons and/or high burst pressure balloons are examples of these types of catheters having stiffer distal end portions. When a stent is positioned over a balloon, the overall stiffness of the distal end portion typically is increased considerably. Other examples of stiffer distal portions are those including a membrane, such as with the balloon, for delivery of pharmaceuticals or treatment materials. Catheters including coated balloons, radiation balloons, laser balloons, or ablation balloons are other examples where trackability is an especially difficult problem in many medical procedures. This situation generally occurs when the distal portion of the catheter embodies an approach which adds a component, and/or increases wall thicknesses and/or reduces material flexibility.
When it comes to tip lengths of balloon dilation catheters, there is a reluctance to extend the length of the distal tip. An elongated tip can impart a perception of a catheter which is too needle-like in appearance. There is also a concern that elongated tips have a tendency to kink when attempting to follow a relatively sharp bend or small radius curve of a flexible guidewire. Accordingly, in many applications, proposals for a longer tip have been met with concern and reluctance to attempt to prepare and use catheters having especially long tips.
At times, balloon catheters are called upon to perform functions in addition to dilatation of lesions and the like. For example, they can be used for delivering and implanting a stent, including applying radial pressure in order to xe2x80x9ctackxe2x80x9d an edge of the stent in place. These and other stents have a high pressure characteristic. Usually, such stent-delivery and/or high-pressure balloon catheters are somewhat stiffer and less flexible than balloon catheters intended for dilatation only. Other balloon catheters which are stiffer and/or less flexible than a typical dilatation catheter such as a percutaneous transluminal coronary angioplasty catheter include the following. Certain catheter designs include balloon membranes which are structured and positioned for delivering treatment pharmaceuticals or other medicaments and the like to specific locations within the body. Other balloon catheters include components, features, thicknesses or materials which bring about a reinforcing or additional feature which reduces pliability. These include catheters having coated balloons, radiation balloons, laser balloons, ablation balloons, and the like. Stiffer balloons along these lines also include balloons for dilatation of large coronary arteries, as well as balloons for primary dilatation of bypass grafts, and for treatment of saphenous veins, carotid peripheral vessels and other non-carotid peripheral vessels. Also in this category are dilatation catheters for neuroradiology. When used herein, these types of catheters are variously referred to as stiffer balloon catheters or balloon catheters having stiffer distal end portions.
These types of stiffer balloon catheters have been found to be associated with problems during delivery, especially when passing over guidewires along a curve or bend in the guidewire. Locations which are especially problematic in this regard include at bifurcation locations, along tortuous paths such as in the atrium, and other similar types of curved paths. If the catheter does not cleanly track over the guidewire, hang-ups tend to occur, resulting in prolapsing of the catheter, such as into the branch of the bifurcated vessel other than the one through which the catheter is passing. Accordingly, there is a need to address kinking difficulties of this type.
Another difficulty with balloon catheter tips involves attempting to maintain the tip to be as atraumatic as possible. In the past, heat sealing and/or attaching procedures have been used which in effect heat treat the entire tip or cause a stiffening at the attachment site. For example, for most materials, a heat treatment results in increased tip stiffness which necessarily detracts from the otherwise atraumatic nature of the material out of which the tip is made.
In accordance with the present invention, problems such as these are addressed through the use of a tip which includes as an important feature thereof a particularly long length. One would expect that a longer length tip would be stiffer because of its longer length (all other factors being equal). One would also expect that a longer tip would not track a guidewire as well as a shorter tip. One would also expect that a longer tip would not make a good radius curve when xe2x80x9ccornering.xe2x80x9d Contrary to these expectations, the present invention enhances tracking and cornering and results in a tip having improved atraumatic properties when compared with other tips made of the same material.
In accordance with the present invention, a balloon catheter is provided which incorporates a longer and especially atraumatic tip. The distal end of the tip member or portion is spaced away from any balloon sealing location so as to avoid or least substantially minimize undesirable heat treatment. The distal edge of the long tip also has an annular chamfer which further enhances the atraumatic nature of the tip. The tip extends distally beyond the distalmost portion of the location at which the balloon is secured to the catheter shaft by a distance of at least about 0.140 inch (about 3.5 mm), and typically not more than about 0.300 inch (about 7.5 mm).
It is accordingly a general object of the present invention to provide an improved balloon catheter having a long and atraumatic tip.
Another object of this invention is to provide an improved balloon catheter which is of the stiffer balloon catheter variety and which tracks well over the guidewire.
Another object of the present invention is to provide an improved balloon catheter which has a stiffer distal end portion and has a long, atraumatic tip which xe2x80x9ccornersxe2x80x9d well when passed over a guidewire, including a PTCA sized guidewire.
Another object of the present invention is to provide an improved balloon catheter which has enhanced path-finding action on the guidewire.
Another object of the present invention is to provide an improved balloon catheter having a tip with a flexibility tailored to the particular need of the catheter.
Another object of this invention is to provide an improved balloon catheter which provides a more gradual increase in distal segment stiffness so as to achieve better tracking of the guidewire through its curves and bends.
Another object of this invention is to provide an improved balloon catheter having a more atraumatic distalmost end.
Another object of the present invention is to provide an improved balloon catheter having a distal portion which provides better position retention should the guidewire be withdrawn too far in a proximal direction.
Another object of this invention is to provide an improved dilatation balloon catheter providing a gradual ramp or wedge structure at its distal end in order to better cross the long axis of a previously deployed stent or to cross through struts or wires of a previously deployed stent, especially when that stent is across a vessel side branch.
These and other objects, features and advantages of the present invention will be apparent from and clearly understood through a consideration of the following detailed description.